Forming‐Free, Nonvolatile, and Flexible Resistive Random‐Access Memory Using Bismuth Iodide/van der Waals Materials Heterostructures

Abstract

next-generation memory devices such as ferroelectric random-access memory, magnetoresistive random-access memory, and resistive random-access memory (RRAM) have been intensively researched and developed. [4-12] Of these innovative nonvolatile memories, RRAM offers low power consumption, fast response speed, long retention time, high scalability, multistate data-storage capability, and a simple metalinsulator-metal structure. [9,13,14] Information storage in the RRAM is achieved by altering the resistance of its insulator. The adjustable resistance of the insulator is achieved by forming metallic or defect filaments with low resistance either by electrochemical metal dissolution or by changing the valence charge of the insulator. [15,16] Generally, the insulator used is either a transition metal oxide or perovskite oxide such as Sr 2 TiO 4 and Cr-doped SrZrO 3. [16,17] However, the synthesis of these materials often requires high temperatures and highly complex fabrication processes that are incompatible with flexible applications. [18,19] Furthermore, a high voltage is required to induce a soft breakdown of the oxide layer, which is detrimental to low-power operation. Lead-based perovskite has recently demonstrated great potential for the fabrication of RRAMs, because of its compact morphology, lowtemperature solution processability, and ionic-transport property. It functions analogously to the human synapse and offers flexible applications with a high on/off ratio, multistate-storage capability, and low set/reset voltage. [13-15,20-27] For example, Choi et al. fabricated an organo-lead halide perovskite RRAM with an on/off ratio of 10 6 , low set/reset voltage of 0.13 V, and four states of information storage. [25] Owing to the high absorption coefficient of perovskite, Zhou demonstrated optoelectronic devices with versatile functions such as photo-sensing, processing, and bit storage with the help of light pulses. [28] However, the structural stability of the perovskite in the air and the issue of its toxicity have led to uncertainty regarding its suitability as a commercial product. [29,30] To solve the issue of toxicity, Park et al. fabricated a zero-dimensional bismuth-based perovskite that had the crystal formula of A 3 Bi 2 I 9 and demonstrated a forming-free device by lowering the defect formation barrier with substitution of sodium into the Bi 3+ cation site. [31] Yang et al. reported forming-free resistive-switching devices Resistive switching devices based on halide perovskites exhibit promising potential in flexible resistive random-access memory (RRAM) owing to low fabrication cost and low processing temperature. However, the toxicity of these materials hinders their commercialization. Herein, bismuth iodide (BiI 3) is employed as an insulator in RRAM. A monolayer of graphene or hexagonal boron nitride (h-BN) is employed as a buffer layer to achieve van der Waals epitaxy of BiI 3 and meanwhile to prevent the intrusion of copper atoms. Thus, the film quality of the BiI 3 layer is greatly improved. Res...

Advances in Flexible Memristors with Hybrid Perovskites

“…In a different approach, Li et al have demonstrated a flexible bismuth iodide (BiI 3 ) memristor using thermal evaporation and CVD techniques (Figure a–c) . The devices, having graphene/copper foil as the electrode, demonstrated a forming-free property and have an ON/OFF ratio of 10 4 with set and reset voltages of 0.3 V and −0.15 V, respectively.…”

“…(a–c) Lead-free flexible memristors: (a) a photograph of the copper foil/graphene/BiI 3 /Au devices, (b) I – V plots and, (c) resistance of the of the BiI 3 memristors as a function of the bending cycle at a bending radius of 8.75 mm. Reprinted with permission from ref . Copyright 2020 John Wiley and Sons.…”

Reliable BiI3-Based Resistive Random-Access Memory Devices with a High On/Off Ratio

“…It demonstrates that there exist metallic states of bismuth atoms at the interfaces between the bismuth iodide and the electrode without bias, which is in a good agreement with the previous literature. 49,50 Moreover, compared to the pristine Ag 3d spectra, the XPS peaks of Ag 3d are initially located at 368.2 and 374.2 eV, as shown in Figure S3, corresponding to 3d 7/2 and 3d 5/2 of metallic Ag. 63 With BiI 3 deposition on the Ag substrate, both peaks are gradually shifted to 367.4 and 374.4 eV, corresponding to the signal of AgI.…”

Coexistence of Write Once Read Many Resistive Switching with Negative Differential Resistance in Bi‐Rich Bi12FeO20 Ideal Sillenite

“…[23] There are reports which potentially demonstrate the WORM properties together with resistive switching in oxide-based materials. [24,25] The bismuth-rich materials, such as BiFeO 3 , BiI 3 , and Bi 4 Ti 3 O 2 [26][27][28] are getting attention for showing memory characteristics. Among these, sillenite Bi 12 MO 20 (M = Fe, Ti, Zn, Ge, etc.)…”